1. Field of the Invention
This invention relates to capture devices for sampling and particularly relates to traveling bucket devices for cutting across a falling stream of particulate material and intermittently capturing a sample thereof.
2. Review of the Prior Art
It has been necessary for many years to obtain reliable samples of particulate materials, such as grain, crushed rock, gravel, sand, ores, coals, particulate or pulverized chemicals, and like materials. In some instances such materials are wet or sticky, so that complete emptying of sampling buckets presents a challenge.
One of the most reliable methods of obtaining representative samples is to take a full cross-section cut from a moving stream of particulate material that is falling from one conveyor to another or from a conveyor to a hopper or bin, or the like. If the particulate material is heterogeneous, such as coal and many ores, collection and handling of samples that adequately represent the bulk lot being transferred requires the collection of increments that are proportional in weight to the flow and evenly distributed over the entire lot. In addition, the amount of some important impurities may determine the size of the sample and the frequency with which the sample is taken from the moving stream of material.
The frequency of the cut through a moving stream of material may be varied according to heterogeneity of the material, the amount of important impurities, the maximum size of the material and the like, but the more frequent the cut, the more representative the sample becomes. However, the amount of material taken from the cut and the frequency of the sampling interval are usually determined by the amount or volume of the material required for sample analysis, the size of the largest particles, the quantity required to produce unbiased results, and on-the-job experience.
With respect to sampling coal, it is equally as important for the seller of a coal as it is for the buyer thereof to know the moisture content, the ash content, and the like at the time and place of transfer from seller to buyer. Environmental regulations within recent years, particularly regarding coal fired electrical generating plants, have also required a reliable knowledge of the coal being burned, so that the coal must be sampled as it is delivered from the mine to the storage yard at the generating plants and from the storage piles to the bunkers that feed the boilers in order to control stack emissions. Moreover, the coal being burned within an electrical generating plant must be constantly sampled in order to maintain proper boiler efficiency.
Such sampling must be done not only in new coal fired generating plants but also in older existing plants which were not designed for coal sampling because it was not required at the time that they were built. Accordingly, coal sampling devices must be added to such older plants in order that they may meet environmental regulations. All such sampling must be done to conform to regulations of the American Society of Testing and Materials or according to some other regulation. For example, ASTM D-2234, entitled "Standard Methods for Collection of a Gross Sample of Coal" must often be followed.
In the past, engineers designed the conveying system with a minimal drop of the coal at transfer points from one conveyor to another or from a conveyor to a coal bunker. In any case, a minimal available height usually limits the addition of retrofit sampling equipment. In most cases, installing such sampling equipment has required a costly raising or lowering of conveyors in order to obtain the required height for installing a sampling device that could extract the required cuts (increments) from the coal flow. There is consequently a need for a sampling device having a minimum of height so that it can be inserted between conveyors or at the dumping point of a conveyor above a coal bunker without requiring a conveyor to be raised or lowered.
U.S. Pat. No. 946,744 discloses a belt conveyor, for conveying ore from one part of an ore treating plant to another, and a pair of sprocket chains which run beneath and beyond the upper end of the belt conveyor while carrying at least one bucket between them. The bucket has a trunnion at each end which is attached to a link of one of the chains and extends beyond the chains to a grooved trolley wheel which runs upon a track so that the bucket is supported at both ends. The bucket is inverted as it passes over a pair of sprocket wheels which carry the chains and dumps its contents into a box or truck.
U.S. Pat. No. 1,155,670 describes a sampling apparatus comprising a plurality of sampling buckets which are attached at the end thereof to a pair of chains that dump the buckets while passing over a pair of sprocket wheels at each end of the chains.
U.S. Pat. No. 1,423,890 describes a sampling apparatus comprising a belt type traveling conveyor having a plurality of openings therein and a sample hopper beneath the end of a discharge chute. All material leaving the chute, such as sand or grain, that falls upon the conveyor belt is carried to the end thereof and dumped into a hopper from which it may be delivered to any desired point. However, all material falling through the opening, as it passes by, drops into a sample hopper so that a desired increment of the falling material is obtained at desired intervals, depending upon the speed of the belt, the size of the openings, and the spacing therebetween.
U.S. Pat. No. 3,472,079 describes an automatic sampling system comprising a batch receiving structure which is disposed beneath the discharge end of the conveyor. The batch receiving structure has an outlet and an exit door and associated timing means for opening and closing the exit door, while stopping the conveyor, after a pre-determined amount has accumulated in the structure.
U.S. Pat. No. 3,524,352 relates to a material sampler which moves a sample bucket, having an adjustable opening, through a stream of falling aggregate at the offbear end of a belt conveyor. The bucket travels longitudinally beneath the belt conveyor and has a pair of stub shafts, attached to its opposite end walls, which are supported by bearing journals attached to a pair of carriage channel brackets supported by two pairs of carriage wheels which ride on a pair of track members. A disc is attached to the end of one stub shaft and has a plurality of projected pegs, which engage teeth in upending plates disposed at the ends of the track members, and a pair of peripheral edge notches, which are engaged by detente means for maintaining the bracket in an upright or upended position.
Some bulk materials that are required to be sampled, particularly coal, can be high in moisture content and thus rather sticky. The cutter opening width in the sample bucket is a function of the maximum size of the particles being sampled. The opening width is generally three times the maximum particle size. The quantity of sample that the bucket must hold is a function of the opening width, quantity of feed, and speed of the traveling bucket. The formula for determining this quantity, i.e., the pounds of material extracted per increment, is as follows: ##EQU1##
When the bucket sampler is in its upside-down discharge position, this wet sticky material may not fully dump, particularly if the relation between the cutter opening width and the bucket width restricts the opening. Therefore, there is a need for a bucket that can aid in dumping wet, sticky material under such conditions.